10 Answers
10

Most probably your interface appears in /etc/network/interfaces. By default, NetworkManager does not manage interfaces that appear in /etc/network/interfaces. You can change this behaviour.

To do this - in a terminal:

sudo nano /etc/NetworkManager/NetworkManager.conf

change the line managed=false to managed=true

Save, stop and start network manager:

sudo service network-manager restart

Alternatively, you can remove the interface from /etc/network/interfaces.

backup the current interfaces file:

sudo cp /etc/network/interfaces /etc/network_interfaces_backup

Then open the file:

sudo nano /etc/network/interfaces

Delete everything in that file and copy and paste the following:

auto lo
iface lo inet loopback

Save, stop and start network manager:

sudo service network-manager restart

Double check in network manager (click on the indicator) that you have Enabled Networking ticked and you should also force deletion of old "wired connections" and selecting the new wired connection shown in the network manager indicator.

Glad to hear it's working. But you also might check out wicd if you have more network troubles. It's in the repo, but you prolly need to do sudo service network-manager stop for wicd to work properly
–
MattOct 24 '11 at 5:29

1

I like the "alternative" method better because it allows you to later edit the network connection from network manager's UI, to specify additional nameservers, DHCP client ID, and 802.1x security settings, etc...
–
SimónMay 23 '14 at 23:56

I had the same problem with a fresh install on my Asus Eee PC 1005HA. The live environment worked with no problems, but once installed I couldn't get the connection to respond or to not read "device not managed". When I changed the text in this configuration file and restarted Network Manager everything worked!

gksudo gedit /etc/NetworkManager/NetworkManager.conf

for lubuntu:

gksudo leafpad /etc/NetworkManager/NetworkManager.conf

Now the text editor will open. Find the line managed=false and replace false with true and save the file (ctrl+s) and close the file.

Restart your computer or the NetworkManager service (sudo service network-manager restart).

Situation like this may appear, when one runs pppoeconf or something similar and the command overwrites the setting saved by NetworkManager. Even though the device seems to be working properly, Network Manager shows device status to be unmanaged.

If this a normal user's pc with simple network configuration like connecting via DHCP and automatic configuration, simply out comment the lines and restart network manager.

In 11.10 you can go to System Settings and you should see a Network Icon. Run that utility and you should see tabs for your network devices, wired and wireless. Each tab has a slider that allows you to switch the device off. Or in your case switch eth0 or wired connection 1, as it is now called, on. May be. At least check that it not switched to off.

sorry but its a no go, there is no slider. I suggest you look at my screenshot. no slider there and I repeat there is nothing in the wired connections tab in my network manager. :(
–
Daniella GloverOct 23 '11 at 21:59

There are two ways to manage network connections. You either have to do everything thru the network manager and remove everything Except the Loopback entry in /etc/network/interfaces

auto lo

iface lo inet loopback

or totally remove the network manager thru the package manager or terminal and use the /etc/network/interfaces and /etc/resolve.conf file to control your connections. If not you will see the error you are getting. Even with static IP I've found that the network manager makes things easy and you can configure your IPV4 connections thru the menu.

This is because the alternate images were for a period of time, configuring the wireless networks in /etc/network/interfaces; which causes NetworkManager to, on purpose, ignore the interface and consider them online.

A good solution if you want to simply use your wireless connection (or wired) with DHCP is to comment out these settings in /etc/network/interfaces for all interfaces except lo, and reboot your system or restart NetworkManager like so:

sudo restart network-manager

Of course, this means you will need to enter your wireless settings into NetworkManager (password, etc) after clicking on the right item from the applet menu.

Just to add a non-default answer, this can also happen if your computer has a hardware ON/OFF switch for the Wi-Fi interface. If you have such a "killswitch", ensure that you haven't accidentally turned the interface off